Synthesis and optical properties of cysteamine-capped ZnS quantum dots for aflatoxin quantification

• A novel and convenient method is developed for aflatoxin quantification.
• The PL intensity variations are in excellent agreement with a Langmuir-type equation.
• The LOD is calculated to be 0.05 ppb which is well below 2 ppb.
• The preparation of colloidal ZnS QDs is cheap and simple.

Water-soluble cysteamine-capped ZnS quantum dots (QDs) are designed to serve as a photodetector for a dangerous group of carcinogens called aflatoxins. ZnS QDs are synthesized by growth in a poly(vinyl alcohol) matrix using the precipitation method. The prepared QDs are characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Our characterization shows that these ZnS QDs have a 1.77 nm crystalline size, cubic zinc blende structure and spherical morphology with a diameter less than 10 nm. Photoluminescence spectroscopy (PL) is performed in the presence of a standard solution of aflatoxins (B1, B2, G1 and G2 with a ratio of 5:1:5:1) at various concentrations, in order to determine the efficacy of a ZnS QD-based aflatoxin detection method. Two PL emission peaks located at 440 nm and 467 nm are observed whose intensities are enhanced by increasing the concentration of total aflatoxin. PL variations in the range of aflatoxin concentrations studied here (2.4 ppb–48 ppb) are best described by a Langmuir-type equation. The limit of detection is calculated to be 0.05 ppb, well below the lowest international contamination allowance in food products.